Cutter inserts for machining and other tools may comprise a layer of polycrystalline diamond (PCD) bonded to a cemented carbide substrate. PCD is an example of a super hard material, also called super abrasive material.
Components comprising PCD are used in a wide variety of tools for cutting, machining, drilling or degrading hard or abrasive materials such as rock, metal, ceramics, composites and wood-containing materials. PCD comprises a mass of substantially inter-grown diamond grains forming a skeletal mass which defines interstices between the diamond grains. PCD material typically comprises at least about 80 volume % of diamond and may be made by subjecting an aggregated mass of diamond grains to an ultra-high pressure of greater than about 5 GPa, typically about 5.5 GPa, and temperature of at least about 1200° C., typically about 1440° C., in the presence of a sintering aid, also referred to as a catalyst material for diamond. Catalyst materials for diamond are understood to be materials that are capable of promoting direct inter-growth of diamond grains at a pressure and temperature condition at which diamond is thermodynamically more stable than graphite.
Catalyst materials for diamond typically include any Group VIII element and common examples are cobalt, iron, nickel and certain alloys including alloys of any of these elements. PCD may be formed on a cobalt-cemented tungsten carbide substrate, which may provide a source of cobalt catalyst material for the PCD. During sintering of the body of PCD material, a constituent of the cemented-carbide substrate, such as cobalt in the case of a cobalt-cemented tungsten carbide substrate, liquefies and sweeps from a region adjacent the volume of diamond particles into interstitial regions between the diamond particles. In this example, the cobalt acts as a catalyst to facilitate the formation of bonded diamond grains. Optionally, a metal-solvent catalyst may be mixed with diamond particles prior to subjecting the diamond particles and substrate to the HPHT process. The interstices within PCD material may at least partly be filled with the catalyst material. The intergrown diamond structure therefore comprises original diamond grains as well as a newly precipitated or re-grown diamond phase, which bridges the original grains. In the final sintered structure, catalyst/solvent material generally remains present within at least some of the interstices that exist between the sintered diamond grains.
A problem known to exist with such conventional PCD compacts is that they are vulnerable to thermal degradation when exposed to elevated temperatures during cutting and/or wear applications. It is believed that this is due, at least in part, to the presence of residual solvent/catalyst material in the microstructural interstices which, due to the differential that exists between the thermal expansion characteristics of the interstitial solvent metal catalyst material and the thermal expansion characteristics of the intercrystalline bonded diamond, is thought to have a detrimental effect on the performance of the PCD compact at high temperatures. Such differential thermal expansion is known to occur at temperatures of about 400[deg.] C., and is believed to cause ruptures to occur in the diamond-to-diamond bonding, and eventually result in the formation of cracks and chips in the PCD structure. The chipping or cracking in the PCD table may degrade the mechanical properties of the cutting element or lead to failure of the cutting element during drilling or cutting operations thereby rendering the PCD structure unsuitable for further use.
Another form of thermal degradation known to exist with conventional PCD materials is one that is also believed to be related to the presence of the solvent metal catalyst in the interstitial regions and the adherence of the solvent metal catalyst to the diamond crystals. Specifically, at high temperatures, diamond grains may undergo a chemical breakdown or back-conversion with the solvent/catalyst. At extremely high temperatures, the solvent metal catalyst is believed to cause an undesired catalyzed phase transformation in diamond such that portions of diamond grains may transform to carbon monoxide, carbon dioxide, graphite, or combinations thereof, thereby degrading the mechanical properties of the PCD material and limiting practical use of the PCD material to about 750[deg.] C.
Attempts at addressing such unwanted forms of thermal degradation in conventional PCD materials are known in the art. Generally, these attempts have focused on the formation of a PCD body having an improved degree of thermal stability when compared to the conventional PCD materials discussed above. One known technique of producing a PCD body having improved thermal stability involves, after forming the PCD body, removing all or a portion of the solvent catalyst material therefrom using, for example, chemical leaching. Removal of the catalyst/binder from the diamond lattice structure renders the polycrystalline diamond layer more heat resistant.
Due to the hostile environment that cutting elements typically operate, cutting elements having cutting layers with improved abrasion resistance, strength and fracture toughness are desired. However, as PCD material is made more wear resistant, for example by removal of the residual catalyst material from interstices in the diamond matrix, it typically becomes more brittle and prone to fracture and therefore tends to have compromised or reduced resistance to spalling.
There is therefore a need to overcome or substantially ameliorate the above-mentioned problems to provide a PCD material having increased resistance to spalling and chipping.